Chapter 7
Sedimentary Rocks
What is a sedimentary rock?
Sedimentary rocks are products of
mechanical and chemical weathering
 They account for about 5% (by volume) of
Earth’s outer 10 miles
 Contain evidence of past environments

• Provide information about sediment
transport
• Often contain fossils
What is a sedimentary rock?

Sedimentary rocks are important for
economic considerations because they may
contain
• Coal
• Petroleum and natural gas
• Sources of iron, aluminum, and manganese
Turning sediment into rock
Many changes occur to sediment after it is
deposited
 Diagenesis = chemical, physical, and
biological changes that take place after
sediments are deposited

• Occurs within the upper few kilometers of
Earth’s crust
Turning sediment into rock

Diagenesis
• Includes
• Recrystallization – development of more stable
minerals from less stable ones
• Lithification – sediments are transformed into
solid rock by
• Compaction and cementation
• Natural cements include calcite, silica, and
iron oxide
Types of sedimentary rocks
Sediment originates from mechanical
and/or chemical weathering
 Rock types are based on the source of the
material

• Detrital rocks – transported sediment as
solid particles
• Chemical rocks – sediment that was once in
solution
Detrital sedimentary rocks

The chief constituents of detrital rocks
include
• Clay minerals
• Quartz-clear or any color
• Feldspars - pink
• Micas – biotite, muscovite

Particle size is used to distinguish among
the various rock types
Detrital sedimentary rocks

Common detrital sedimentary rocks
• Shale
• Mud-sized particles in thin layers that are
commonly referred to as laminea
• Most common sedimentary rock
• Sandstone
• Composed of sand-sized particles
• Forms in a variety of environments
• Quartz is the predominant mineral
Laminae = layers about 1
cm thick or less
Shale with plant remains
Figure 7.2
Quartz sandstone
Figure 7.4
Detrital sedimentary rocks
• Conglomerate and breccia
• Both are composed of particles greater than
2mm in diameter
• Conglomerate consists largely of rounded
gravels
• Breccia is composed mainly of large angular
particles
Conglomerate
Figure 7.6
Breccia
Figure 7.7
Chemical sedimentary rocks

Consist of precipitated material that was
once in solution

Precipitation of material occurs by
• Inorganic processes
• Organic processes (biochemical origin)
Chemical sedimentary rocks

Common chemical sedimentary rocks
• Limestone
• Most abundant chemical rock
• Composed chiefly of the mineral calcite
• Marine biochemical limestones form as coral
reefs, coquina (broken shells), and chalk
(microscopic organisms)
• Inorganic limestones include travertine and
oolitic limestone
Coquina
Figure 7.9
Fossiliferous limestone
Chemical sedimentary rocks

Common chemical sedimentary rocks
• Dolostone
• Typically formed secondarily from limestone
• Chert
• Composed of microcrystalline quartz
• Varieties include flint and jasper (banded form
is called agate)
Agate
Figure 7.12 A
Chemical sedimentary rocks

Common chemical sedimentary rocks
• Evaporites
• Evaporation triggers deposition of chemical
precipitates
• Examples include rock salt and rock gypsum
Chemical sedimentary rocks

Common chemical sedimentary rocks
• Coal
• Different from other rocks because it is
composed of organic material
• Stages in coal formation (in order)
• 1. Plant material
• 2. Peat
• 3. Lignite
• 4. Bituminous
Stages
of
coal
formation
Figure 7.15
Stages
of
coal
formation
Figure 7.15
Classification of
sedimentary rocks
Sedimentary rocks are classified according
to the type of material
 Two major groups

• Detrital
• Chemical
Classification of
sedimentary rocks

Two major textures are used in the
classification of sedimentary rocks
• Clastic
• Discrete fragments and particles
• All detrital rocks have a clastic texture
• Nonclastic
• Pattern of interlocking crystals
• May resemble an igneous rock
Identification of
sedimentary rocks
Figure 7.17
Sedimentary environments
A geographic setting where sediment is
accumulating
 Determines the nature of the sediments that
accumulate (grain size, grain shape, etc.)

Sedimentary environments

Types of sedimentary environments
• Continental
• Dominated by stream erosion and deposition
• Glacial
• Wind (eolian)
• Marine
• Shallow (to about 200 meters)
• Deep (seaward of continental shelves)
Sedimentary environments
• Transitional (shoreline)
• Tidal flats
• Lagoons
• Deltas
Sedimentary
environments
Figure 7.19 (left)
Sedimentary
environments
Figure 7.19 (right)
Sedimentary environments

Sedimentary facies
• Different sediments often accumulate
adjacent to one another at the same time
• Each unit (called a facies) possesses a
distinctive set of characteristics reflecting
the conditions of a particular environment
• The merging of adjacent facies is a gradual
transition
Sedimentary facies
Figure 7.20
Sedimentary structures
Provide information useful in the
interpretation of Earth history
 Types of sedimentary structures

• Strata, or beds (most characteristic of
sedimentary rocks)
• Bedding planes that separate strata
• Cross-bedding
Sedimentary structures

Types of sedimentary structures
• Graded beds
• Ripple marks
• Mud cracks
• Fossils
End of Chapter 7